docs: def CreateConstMuskingumXFile(x_value,
                                in_connectivity_file,
                                out_x_file):
      """
      Create muskingum X file from value that is constant all the way through
      for each river segment.
  
      Parameters
      ----------
      x_value: float
          Value for the muskingum X parameter [0-0.5].
      in_connectivity_file: str
          The path to the RAPID connectivity file.
      out_x_file: str
          The path to the output x file.
  
  
      Example::
  
          from RAPIDpy.gis.muskingum import CreateConstMuskingumXFile
  
          CreateConstMuskingumXFile(
              x_value=0.3,
              in_connectivity_file='/path/to/rapid_connect.csv',
              out_x_file='/path/to/x.csv')
  
      """
      num_rivers = 0
      with open_csv(in_connectivity_file, "r") as csvfile:
          reader = csv_reader(csvfile)
          for _ in reader:
              num_rivers += 1
  
      with open_csv(out_x_file, 'w') as kfile:
          x_writer = csv_writer(kfile)
          for _ in xrange(num_rivers):
              x_writer.writerow([x_value])